Petroleum jelly is a tried and tested constituent of many cosmetic and/or pharmaceutical bases for topical application. It is used very widely in leave-on and rinse-off preparations, as the basis of creams and ointments and can, for example, also be used in shower baths.
Petroleum jelly belongs to the hydrocarbon gels and is a two-phase system with 70 to 90% of a liquid phase of n- and isoparaffins and olefin hydrocarbons such as cetene, heptadecene and octadecene, and also 10 to 30% of a solid phase. The solid phase consists of a microcrystalline fraction predominantly of isoparaffins and small fractions of alicycles and a crystalline fraction of n-paraffins. The gel structure of petroleum jelly arises as a result of the formation of a framework which is formed by the longer-chain solid paraffins. These position themselves—held via van der Waals-London forces—in parallel with one another and form so-called fringed micelles since the ends of the long-chain paraffins protrude unevenly from the micelle and contribute in part to the formation of further micelles. This produces a three-dimensional framework by virtue of numerous linked-together islands of parallel long-chain paraffins into which the liquid hydrocarbons are intercalated. The corresponding composition of crystalline, microcrystalline regions and liquid hydrocarbons determines the formation of this gel structure and thus the particular rheological properties (plasticity, ductility) of petroleum jelly.
Petroleum jelly is characterized by a very wide melting range and behaves largely neutrally in chemical terms.
Predominantly, naturally obtained petroleum jelly is used in cosmetic and pharmaceutical preparations; this is a mixture of n-paraffins, isoparaffins and hydroaromatic hydrocarbons that is produced in the residue during the refining of petroleum and which is purified by treating with concentrated sulfuric acid and bleaching earths and/or activated carbon. Different grades of petroleum jelly are produced depending on the type of purification. However, there likewise also exists a synthetically produced petroleum jelly which is obtained by dissolving paraffin and ceresin in liquid paraffin.
However, it is known that paraffins can accummulate, depending on chain length, in the liver, lymph nodes and kidneys. Time and again, it is discussed how mineral oils, being fats that are difficult to degrade, lead to an accumulation in the body and, as a result of closing the skin pores, impair the breathing of the skin or promote the development of acne. Lip care sticks containing mineral oils have therefore also already been criticized.
Despite the known good topical compatibility of paraffins, there is a continuing interest in preparations which comprise ointment bases which are characterized by production from renewable raw materials. In terms of properties, they should correspond to those of petroleum jelly. Bases hitherto for replacing petroleum jelly have relatively narrow melting ranges, and therefore the search was for possible substitute bases with a comparable broad melting range.
Even some years ago, the mixture of beeswax and plant oil served as petroleum jelly substitute. However, beeswax, being a natural product, cannot in the short term be produced in large amounts.
The international application WO 2007/107966 discloses deodorant preparations which comprise hydrogenated castor oil as petroleum jelly substitute, which is lowered in its viscosity by castor seed oil, liquid fatty alcohols and plant oils. It is assumed that fragrances remain for longer in these cosmetic bases compared with in the petroleum jelly-based preparations on account of the higher polarity of hydrogenated castor oil.
The synthesis of ethers from alcohols is a long-established process in the chemical industry. Short-chain ethers can be used as solvents. The condensation of primary alcohols can be catalyzed e.g. by acids or bases; ethers are formed as reaction product.
For instance, there are various ethers available on the cosmetics market, e.g. Cetiol OE® from BASF Personal Care and Nutrition GmbH.
Sasol has various Cosmacol® ethers on the market [“Sasol Raw Materials for Cosmetics”. Sasol Olefins & Surfactants GmbH Anckelmannsplatz 1, 20537 Hamburg, Germany], e.g. COSMACOL® OE (Dioctyl ether), COSMACOL® Ether 10 (Didecyl Ether), COSMACOL® Ether 12 (Dilauryl Ether), COSMACOL® Ether 14 (Dimyristyl Ether), COSMACOL® Ether 16 (Dihexadecyl ether) and COSMACOL® SE (Distearyl ether) [“Sasol Raw Materials for Cosmetics”. Sasol Olefins & Surfactants GmbH Anckelmannsplatz 1, 20537 Hamburg, Germany].
A diisononyl ether is on the market from Nikko Chemicals (Nikkol DINE)
A common feature of these ethers is that they are only pure compounds with a defined melt behavior.
Some short-chain ethers are liquid at room temperature. They can be used for example as cosmetic emollients. Longer-chain C18 ethers are solid and have a high melting point in the range >45-50° C. High-melting compounds generally have a clearly defined melting point and are therefore not suitable as petroleum jelly substitute.